Coding signal relay system



June 23, 1964 A. HUFNAGEL CODING SIGNAL RELAY SYSTEM 3 Sheets-Sheet 1 Filed Feb. 2. 1960 United States Patent 3,138,680 CODING SIGNAL RELAY SYSTEM Andrew Hutnagel, Penn Hills Township, Allegheny County, Pa., assignor to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Filed Feb. 2, 1960-, Ser. No. 6,152 Claims. (Cl. 20090) My invention relates to electrical relays, and particularly to electrical relays which are suitable for use in railway signaling systems employing for the control of signalmg devices direct current which is periodically interrupted or coded at different frequencies in accordance with traffic conditions.

More particularly, my present invention relates to improvements in relays of the type described in Letters Patent of the United States No. 2,426,970, granted tome on September 2, 1947, for Electrical Relay, in which a compound pendulum mechanically coupled with a contact carrying rocker of the relay is provided for controlling the rate of operation of the relay. The mechanical coupling between the pendulum and the rocker comprises a vertical arm, the upper end of which is connected to the rocker and the lower end of which is operatively connected with the pendulum in such a manner that the rocker is caused to oscillate in synchronism with the oscillations of the pendulum. Due to the intermediate connection provided by the arm, and the arrangement of the parts, rotation of the pendulum in one direction will cause swinging movement of the rocker in the opposite direction. While the operation of the relay in the reference patent has been in all respects most satisfactory, a relay of this type embodying the intermediate arm is generally large in overall size, and one object of my present invention is to provide an improved relay of smaller vertical dimension by eliminating the intermediate arm and mounting the relay contacts directly on the pendulum structure.

Another object of my invention is to provide a code transmitting relay comprising a single oscillating part, thereby enabling greater economy in both manufacture and operation.

Other objects and features of my invention will become apparent as the specification proceeds.

In accordance with my invention, I employ a contact carrying rocker mounted for swinging movement between two extreme positions and an electromagnet for oscillating a compound pendulum suspended from the rocker, the energization of the electromagnet being controlled by contacts mounted directly on the rocker. In addition to the contacts for controlling the energization of the electromagnet, I provide other contacts also mounted on the rocker and arranged to cooperate with fixed contacts mounted on an adjacent insulating plate, whereby a first contact closure is effected when the rocker is swung by the pendulum toward its one extreme position and a second contact closure is effected when the rocker is swung toward its other extreme position.

I shall describe one form of electrical relay embodying my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawings,

FIG. 1 is a side elevational View partially in section of a relay in accordance with my invention.

FIG. 2 is a front elevational view of the relay shown in FIG. 1.

FIG. 3 is a top view showing one form of contact carrying rocker embodying my invention as applied to the relay shown in FIGS. 1 and 2.

FIG. 4 is a side elevational view of the contact carrying rocker shown in FIG. 3.

FIG. 5 is another view of the contact carrying rocker 3,138,680 Patented June 23, 1964 embodying my invention as it appears when viewed from the right in FIG. 4.

FIG. 6 is a view showing the mounting bracket for sluppgrging the operating parts of the relay shown in FIGS.

FIG. 7 is a top plan view of the relay shown in FIG. 1 with certain of the parts removed.

Similar reference characters refer to similar parts in each of the several views.

Referring now to the drawings, the relay which is designated as a whole by the reference character 10 comprises a frame member 12 of suitable nonmagnetic material, such as aluminum, having a vertical portion and two horizontal forwardly extending portions 12b and 120 (FIG. 2) disposed on opposite sides of the relay. The portions 12b and 120 of frame member 12 are each formed at the upper sides thereof with a transverse inwardly extending supporting rib 120', which ribs are best seen in FIGS. 2 and 7. The operating parts of the relay are all enclosed within a suitable case consisting of a transparent cover 14 secured to portions 12b and 120 at the front of the relay by suitable screws 15 (FIG. 7). At the upper and lower sides of the relay, gaskets 16 of cork or other suitable material are imposed between the ends of cover 14 and portion 12a of frame member 12, thereby sealing the relay against the entry of dirt or other foreign substances. The relay of the present invention is adapted for plug-in application in a stationary mounting base or receptacle (not shown) of the type well known in the art, and a pair of indexing pins 18 is provided in a well-known manner to align the relay with its mounting base to prevent errors in replacement.

A mounting bracket 20 of one piece (FIG. 6) is provided for supporting the operating parts of the relay. This mounting bracket comprises two spaced parallel por tions 20a and 20b afiixed as by screws 22 (FIGS. 2 and 7) to the undersides of ribs 12d of the portions 12b and 120 of frame member 12. The lower portion of bracket 20 includes connecting portions 20c and 20d joined with portions 20a and 20b by upstanding arms 20e to form a quadrangular space bounded by portions 20a and 20b and connecting portions 20c and 20d, of bracket 20.

As best seen in FIGS. 2 and 7, two oppositely disposed fixed contact supports 24 and 26 of generally rectangular configuration and of suitable insulating material, such as a phenyl condensation product, are mounted by screws 28 on the upper sides of portions 20a and 20b of bracket 20. The contact supports 24 and 26 are provided with a plurality of fixed contact fingers 30 and 30a adjustably mounted by nuts 34 on terminal posts 36. Also secured to the terminal posts by the same nuts 34 which affix the contact fingers thereto are terminals 38 and 40 for electrically connecting the contact fingers with suitable lead-in wires not shown. The posts 36 are secured to confronting sides of contact supports 24 and 26 by means of screws 42 (FIGS. 1 and 7) disposed within semicircular grooves 44 formed in the contact supports. The screws 42 extend with appreciable clearance through suitable holes in the contact supports and engage tapped holes in the terminal posts 36. The screws 42 are thus capable of being positioned relative to the contact supports to allow adjustment of the terminal posts in order to maintain the contact fingers supported thereby in desired vertical and longitudinal positions.

The relay also comprises a contact carrying rocker of suitable insulating material (FIGS. 3, 4 and 5) designated by the reference character 46, and having a substantially rectangular configuration. The rocker 46 is molded on a horizontally disposed bearing shaft 48, to be described, and is arranged with its longitudinal axis parallel with portions 20a and 20b of mounting bracket 20. The rocker extends downwardly within the quadrangular space surrounded by the aforementioned portions of the mounting bracket and, as best seen in FIG. 2, has its lower end spaced slightly from the upper surface of connecting por' tions c and 20d of bracket 20 to allow it to swing without interference. On opposite sides of rocker 46 there is provided a plurality of flexible contact fingers 50 and 50a secured to the rocker at their lower ends as by screws 52 and metal washers 54. Each of the contact fingers extends alongside and upwardly from the base of the rocker in a substantially vertical plane, and is provided adjacent its free or upper end with a contact element offset slightly from a point directly above the axis of rotation of the 'rocker and cooperating with fixed contact fingers or 30a to close a contact 30-50a or 30a-50 accordingly as the rocker is swung to one or the other of its extreme positions. Connections from contactfingers and 50:: are provided by flexible connecting strips 56 and 58 having their one end electrically connected with the movable contact fingers by the screws 52 and washers 54. The other ends of strips 56 and 58 are disposed in suitable grooves provided in contact supports 24 and 26, and are afiixed to the contact supports by means of screws 60 (FIG. 2) and other metal spacers 62 which, in turn, electrically connect the connecting strips with terminals or lugs 64 to which wires from external circuits can be connected. The strips 56 and 58 are bent to respectively form relatively long portions 56a and 58a inclined upwardly away from and in oblique relation to the sides of the rocker, and horizontal portions 56b and 58b disposed in superposed spaced relation substantially normal to the axis of the shaft. The purpose of the above-described configuration of the connecting strips will be made clear hereinafter.

The relay also comprises motor means for oscillating the rocker between its two extreme positions to alternately operate the contacts at a constant preselected frequency. As here shown, these motor means comprise an electromagnet C comprising a core 66 surrounded by a winding 68 and having pole pieces 70 and 70a secured by means of screws 72 to the ends of core 66 in parallel spaced relation. The ends of core 66 extend through suitable holes in the connecting portions 200 and 20d of mounting bracket 24), only one of these holes 20] being shown in the drawings (FIGS. 2 and 6). Screws 74 extend upwardly through suitable threaded holes 20i in the connecting portions of bracket 20 and engage the core ends to firmly secure them in place. The pole pieces 70 and 70a of electromagnet C cooperate at their lower or free ends with a magnetizable armature 76 secured to one side of a lower portion or foot 78 of a compound pendulum P. The compound pendulum P may have any suitable form possessing within the limited space available the necessary mass to cause it to have a natural period equal to the deslred code frequency, which may, for example, be 180 cycles per minute. In the form here illustrated, this pendulum comprises a central depending leg 80 secured to one side of the rocker 46 at its upper end, as by screws 82 engaging suitable threaded holes in the rocker, and terminating at its lower end in foot 78 to which the armature 76, referred to hereinabove, is secured.

Each of the ends of the bearing shaft 48 supporting the rocker 46 rests on a pair of crossed bearing tracks 84 provided on the upper ends of laterally offset bearing arms 86. The bearing arms 86 are in line toward the shaft so that the planes of the arms intersect substantially at the axis of the shaft, and are each provided at their lower ends with a flexible supporting strip 88 which is secured at its lower end by means of an associated screw 90 to an inclined surface 20g formed on a bearing mounting block 20h of mounting bracket 20. The arrangement of the bearing arms is such that the supporting strip 88 will flex in the form of a gradual curve in response to movement of the bearing arms due to operation of the pendulum.

parallel spaced relation (FIG. 1).

The bearing tracks are so disposed that they are substantially normal to the plane of the arm, and the angles at which the arms are disposed are such and the parts are so proportioned that when the pendulum is moved in either direction from its gravity biased position, the frictional adhesion between the ends of the shaft and bearing tracks will cause the tracks to move with the ends of the shaft in such manner that substantially pure rolling motion results, the necessary motion of the tracks being permitted by the flexing of the flexible supporting strips. It will be seen, therefore, that oscillation of the pendulum will cause a new line of contact to be formed between each end of the shaft and each track in each diiferent angular position of the pendulum throughout its entire angular movement.

The pendulum is maintained in the desired longitudinal position relative to the bearing tracks and to the pole pieces of the electromagnet by means of plates 92 in The plates 92 are secured to the connecting portions 20c and 20d of the mounting bracket as by screws 96, and extend upwardly past the shaft to positions a slight distance above the ends of the shaft. The plates 92 are intended tobe so adjusted that when the pendulum is in the proper longitudinal position, the plates will just clear the ends of the shaft. To reduce friction and wear, the ends of the shaft are rounded and along with the upper ends of plates 92 they may be chromium plated.

Excessive vertical displacement of the pendulum P from its normal position is prevented by passing the ends of the shaft through suitable clearance holes 97 (FIG. 2) provided in the upper ends of other plates 98 disposed similarly in parallel spaced relation. The same screws 96 which secure the first mentioned plates 92 to the mounting bracket also affix plates 98 to the mounting bracket. The clearance holes 97 are made sufficiently large that they do not interfere in any way with the normal angular movement of the pendulum, but that, if due to handling or the like, abnormal forces are exerted on the pendulum, the shaft will strike the edges of the holes in plates 98 and will thus act to limit the displacement of the pendulum to an amount which is insuflicient to cause any damage to the parts.

With the pendulum suspended from the rocker in the manner just described, it will be apparent that rotation of the pendulum in one direction will cause swinging movement of the rocker in the same direction, and the parts are further so proportioned that oscillation of the pendulum through its normal amplitude will cause movement of the rocker between its two extreme positions. The length of the pendulum is such that armature 76 is free to swing between the pole pieces 70 and 70a. It will be seen, therefore, that energization of the winding 68 will tend to pull the armature between the pole pieces, and hence, will initially swing the pendulum and the rocker in a clockwise direction, as viewed in FIG. 2.

Preferably, the energization of winding 68 is controlled by other movable contact fingers 102 and 104 located on the rocker intermediate the two innermost contact fingers 50 and 50a, and having suitable contact elements at their upper ends cooperating with fixed contact fingers 30 or 30a to form two sets of contacts 30a-102 and 30104 connected in series with the winding of the relay. The lower ends of contact fingers 102 and 104 are secured to rocker 46 as by screws 106 (FIG. 4) and electrically interconnected by a jumper strap 108 of conductive material. The contact fingers 102 and 104 are so positioned that both contacts 30a102 and 30-104 are closed when the pendulum occupies its gravity-biased position, but that when the pendulum is swung away from this position, one or the other of these contacts will become opened at a predetermined point in the stroke of the pendulum depending upon the direction in which the pendulum is swung.

It will be obvious that oscillation of the pendulum will cause the contacts 30-50a and 30a-50, which are not used to control the energization of winding 68, to be alternately opened and closed at the frequency of oscillation of the pendulum. These contacts may be used for coding purposes, or for any other desired purpose, as will be readily understood.

In addition to being electrically conducting, the connecting strips 56 and 58 are made of spring material which enables them to exert a continuous downward force on the rocker when they are installed in the relay. The connecting strips are manufactured to have, when free, the shape shown in FIG. 5, in which the uppermost portions of the strips are substantially horizontal. When the connecting strips are installed in the relay they will assume the slightly different configuration shown in FIG. 2, the uppermost portions having a displacement from horizontal which is indicative of the downward force being exerted on the rocker. As the rocker moves from its at-rest position, this downward force provided by the connecting strips will act to augment the frictional adhesion required between the ends of the shaft and the bearing tracks to ensure a pure rolling motion of the shaft. The advantage of thus transmitting the bias developed in the horizontal portions of the connecting strips from the strips through the rocker and thence to the shaft becomes apparent during operation at higher code frequencies. That is, to increase the code frequency it is generally the practice in the art to reduce the mass of the pendulum, which expedient, obviously reduces the force for maintaining the shaft firmly centered during movement of the pendulum. It will be appreciated, therefore, that in the present invention no adjustment is necessary to obtain consistent pressure forcing the shaft against the bearing tracks at higher code frequencies, and that it is a relatively simple matter to manufacture the bent connecting strips so as to obtain the required pressure. Moreover, due to the relatively large length of the oblique portions of the connecting strips, stresses developed in the connecting strips during flexing that otherwise might be damaging in shorter strips will easily be relieved, whereby the probability of fatigue or permanent set occurring in the metal will be practically eliminated.

As previously mentioned, when winding 68 becomes energized, the pendulum will swing to the left, as oriented in FIG. 2, which motion causes rocker 46 to close the gap between fixed contact fingers 30a and the contact elements of movable contact fingers 50, and increase the spacing between the other movable contact fingers 50a and their associated fixed contact fingers 30. Continuing angular movement of the rocker toward its one extreme position decreases the distance separating the tip end of fixed contact fingers 30a and the point on rocker 46 to which contact fingers 50 are secured, with the result that the contact elements of contact fingers 50 will move, but only slightly, vertically in an upward direction over contact fingers 30a after their mutual engagement. After the momentum of the pendulum is expended, it will start its return swing and, accordingly, by swinging the rocker in the opposite, or counterclockwise direction, cause the contact elements of contact fingers 50 to move downwardly over contact fingers 30a until the point of contact separation is reached. Each of the other movable contact fingers 50a will cooperate with its associated contact finger 30 in an entirely similar manner during the other half cycle of pendulum movement. The parts are so proportioned that the forward and backward rubbing activity between the contact elements of the movable contact fingers and their associated contact fingers is insuificient to cause abnormal wear or deterioration, but is sufiicient to provide a self-cleaning effect and, hence, smooth and low resistance contact surfaces. It will be obvious that due to the sliding cooperation between mating contacts, as illustrated in the present construction, any sticking of contacts will be less likely to occur.

In a similar manner, each of contact fingers 102 and 104 for controlling the energization of winding 68 will cooperate with its associated fixed contact fingers 30 or 30a to effect self-polishing of their contact surfaces. In this case, however, it will be evident that the upward movement of the contact elements of contact fingers 102 and 104 relative to their corresponding fixed contact fingers will occur substantially immediately as the rocker begins to swing, and will continue until the rocker reverses its movement. Similarly, during return motion of the rocker, the frictional engagement between the contact surfaces will be continuous but, as will be realized, relative movement of the contact surfaces will be reversed. In this way, as previously explained, any likelihood of undesirable aspects of contact action appearing will be minimized.

As will be apparent from an inspection of the drawings, the pendulum possesses considerable mass, and to prevent it from swinging and other movements during handling of the relay which might cause damage to the bearing arms and to the other parts of the relay, I provide a shipping lock for the relay comprising a rod 109 of considerable length and rigidly affixed to or forming a part of a screw 110. The pendulum armature 76 is provided at opposite ends with upstanding arms 112 (FIG. 2), each provided at its upper end with a portion 112a having suitable clearance holes aligned with each other, and secured at its lower end to the armature 76 by screws 114. The arms 112 are so positioned that when the pendulum occupies its gravity-biased position and the shipping lock is applied, the rod 109 will enter the holes in portions 112a of the arms 112 and extend at its far end through an aligned hole 92a in the right-hand one of the plates 92, as shown in FIG. 1. In this position, the pendulum is locked against movement. It will be seen, therefore, that all parts of the relay will then be protected from damage which might otherwise result if the movement of the pendulum were not prevented. The screw 110 is arranged to lock the shipping lock in this holding position by cooperating with a threaded hole in the vertical portion 12a of frame member 12.

When it is subsequently desired to place the relay in operation, the shipping lock is removed and the hole in portion 12a of the frame member 12 is filled with a suitable plug (not shown) which may, for example, comprise a short screw.

From the foregoing description, it can be seen that a principal advantage of a relay embodying my invention is that the overall height of the relay is reduced, thereby permitting it to be used in relay housings or cases in which compactness and economy of space is desired.

Another advantage of a relay embodying my invention is that the simplified construction of a single moving part results in reducing the manufacturing costs of the relay.

Still another advantage of a relay embodying my invention is that on account of the reduced number of movable parts, the reliability of operation of the relay will be improved and its service life extended.

Yet another advantage of a relay embodying my invention is that the contact area of each electrical contact is cleaned automatically during engagement with its associated contact, thereby prolonging the period of time that the contacts will reliably operate.

Although I have herein shown and described only one form of electrical relay embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. A relay comprising a rotatable shaft, bearing means cooperating with the ends of said shaft for horizontally disposing it to revolve on its axis about a fixed point, a rocker of insulating material fixedly attached to said shaft, a pendulum suspended from said rocker, said pendulum normally occupying a gravity-biased position, means for oscillating said pendulum whereby said rocker is revolved on said axis between two extreme positions, a fixed contact finger, and a flexible contact finger secured at one end to saidrocker and at its free end normally spaced from said fixed contact finger in a manner to engage said fixed contact finger at substantially the instant said rocker begins to swing toward one of its extreme positions, the

parts being so disposed and arranged that following the mutual engagement of said contact fingers the free end of said flexible contact finger slides over said fixed contact vfinger in one direction during movement of said rocker toward said one extreme position and slides over said fixed contact finger in the opposite direction during movement of said rocker away from said one extreme position;

2. In an electrical relay, a shaft mounted to revolve on its axis about a fixed point and having its axis oriented horizontally, a rocker of insulating material secured to .said shaft for rotation therewith, said rocker presenting substantially plane and vertical faces on opposite sides of the longitudinal axis of said shaft, a pendulum so connected with said rocker that said rocker is swung between two extreme positions in response to angular movement of said pendulum, means for oscillating said pendulum,

a first and a second flexible contact finger, said first and second contact fingers being disposed alongside one and the other faces of said rocker respectively and each being rocker is at rest, the parts being so proportioned that the free end of each of said contact fingers alternatelyengages the contact member adjacent thereto by a slightly sliding movement when said rocker is in motion.

3. In an electrical relay including a rotatable shaft, a

rocker secured to said shaft, a pendulum secured to said rocker, a mounting bracket, a pair of bearing arms extending toward each end of said shaft on opposite sides thereof, each of said arms being secured at its lower end to a flexible strip connecting with said mounting bracket and being provided at its upper end with a bearing track extending normal to the plane of the arm adjacent the associated end of said shaft, the two tracks on the arms of each pair being laterally offset and supporting one end of said shaft, contacts controlled by said rocker, means controlled by said contacts for causing said pendulum to oscillate whereby said rocker is swung between two extreme positions, at least two flexible contact fingers each mounted on said rocker and on opposite sides of the longitudinal axis of said shaft, second contacts alternately operated by said contact fingers according as said rocker swings between its extreme positions, and flexible electrically conducting strips each secured at its lower end to one of said contact fingers and at its free end being fixed with respect to said rocker, each of said strips consisting of a portion inclined upwardly from said rocker in oblique relation therewith and a continuous outwardly extending generally horizontal portion disposed substan= tially normal to the axis of said shaft, whereby when said rocker is in motion the horizontal portion of each of said stripswill not only flex but will also exert a substantially downward thrust on said shaft through said rocker acting to maintain the ends of said shaft properlytpositioned against their associated bearing tracks.

4. In an electrical relay, the combination of a rotatable shaft and a rocker molded on said shaft, a pendulum secured, at one end to said rocker and at its lowerend having an armature attached thereto, a mounting bracket for supporting the parts of said relay and provided with LL} spaced parallel portions provided with aligned clearance holes and with threaded holes communicating with each of said clearance holes, a pair of bearing arms extending toward each end of said shaft on opposite sides thereof,

each of said arms being secured at its lower end to a flexible strip connecting with said mounting bracket and being provided at its upper end with a bearing track extending normal to the plane of the arm adjacent the associated end of said shaft, the two tracks of each pair being .laterally offset and supporting one end of said shaft, an

electromagnet including spaced pole pieces and a core having a winding thereon, said armature being disposed vto swing between said pole pieces, each of the ends of said core projecting through a clearance hole in said portions of saidmounting bracket, a screw threadably engaging each threaded hole in said portions of said mounting bracket and abutting on one end of said core to rigidly mount said electromagnet in position, contacts carried by said rocker, and contact means controlled by said contacts for energizing said electromagnet winding to cause said pendulum to oscillate at substantially-its natoperate with said pole pieces in response to the energization of said electromagnet so as to cause said pendulum to oscillate, means controlled by said rocker for applying electrical energy to said electromagnet for alternately energizing and deenergizing it, a mounting bracket, a first and a second insulating contact support mounted on said bracket and disposed on opposite sides of the longitudinal axis of said shaft, first and second contact members fixedly mounted on said first and second contact supports respectively, said rocker having first and second flexible contact fingers thereon each being spaced normally from one of said contact members and being adapted to engage the contactmember associated therewith each time said rocker swings toward a preselected one of its extreme positions, first and second flexible strips of conductive material disposed on opposite sides of the axis of said shaft and being electrically connected at one end to said first and second contact finger respectively, and each being fixed at its free end to one of said contact supports, each strip intermediate its ends having a portion extending upwardly from and in oblique relation to said rocker and an uppermost generally horizontal portion extending rearwardly from and substantially normal to the axis of said shaft, the uppermost portions of said strips being arranged to exert a continuous downward force on said shaft through said rocker to retain the journaled portions of said shaft in proper cooperating relation to their corresponding bearings when said rocker is in motion.

References Cited in the file of this patent UNITED STATES PATENTS Stolp a May 16, 1916 1,537,796 Bossard et a1 May 12, 1925 2,156,684 Fisher et al May 2, 1939 2,156,685 Shaw May 2, 1939 2,337,205 Mishelevich Dec. 21, 1943 2,374,727 Blosser May 1, 1945 2,435,000 Field Jan. 27, 1948 2,845,508 Lockett July 29, 1958 2,916,582 Hufnagel Dec. 8, 1959 

1. A RELAY COMPRISING A ROTATABLE SHAFT, BEARING MEANS COOPERATING WITH THE ENDS OF SAID SHAFT FOR HORIZONTALLY DISPOSING IT TO REVOLVE ON ITS AXIS ABOUT A FIXED POINT, A ROCKER OF INSULATING MATERIAL FIXEDLY ATTACHED TO SAID SHAFT, A PENDULUM SUSPENDED FROM SAID ROCKER, SAID PENDULUM NORMALLY OCCUPYING A GRAVITY-BIASED POSITION, MEANS FOR OSCILLATING SAID PENDULUM WHEREBY SAID ROCKER IS REVOLVED ON SAID AXIS BETWEEN TWO EXTREME POSITIONS, A FIXED CONTACT FINGER, AND A FLEXIBLE CONTACT FINGER SECURED AT ONE END TO SAID ROCKER AND AT ITS FREE END NORMALLY SPACED FROM SAID FIXED CONTACT FINGER IN A MANNER TO ENGAGE SAID FIXED CONTACT FINGER AT SUBSTANTIALLY THE INSTANT SAID ROCKER BEGINS TO SWING TOWARD ONE OF ITS EXTREME POSITIONS, THE PARTS BEING SO DISPOSED AND ARRANGED THAT FOLLOWING THE MUTUAL ENGAGEMENT OF SAID CONTACT FINGERS THE FREE END OF SAID FLEXIBLE CONTACT FINGER SLIDES OVER SAID FIXED CONTACT FINGER IN ONE DIRECTION DURING MOVEMENT OF SAID ROCKER TOWARD SAID ONE EXTREME POSITION AND SLIDES OVER SAID FIXED CONTACT FINGER IN THE OPPOSITE DIRECTION DURING MOVEMENT OF SAID ROCKER AWAY FROM SAID ONE EXTREME POSITION. 